1. Field of the Invention
This invention relates to conveying and supporting rolls, and more particularly, to rolls for use in glass annealing lehrs.
2. Discussion of the Presently Available Technology
Rolls for supporting and conveying sheet material at elevated temperatures are of interest in the glass industry. Of particular interest in this discussion are rolls for conveying and supporting a glass ribbon as it advances through an annealing furnace or heat treating furnace. The glass ribbon usually enters the furnace or lehr at a temperature of about 1000.degree. F. (537.8.degree. C.) and exits at a temperature of about 400.degree. F. (204.4.degree. C.).
U.S. Pat. No. 2,428,344 teaches a conveying roll, which in general, includes a metal core, an outer tubular body of refractory material surrounding and spaced from the core. Heat insulating material in the form of a hardened and set mass of cement fills the outer tubular body and bonds the core to the outer body to provide a unitary structure. Although the above roll is acceptable, there are limitations. More particularly, the roll has a unitary construction, therefore damage to any portion of the roll, e.g., surface damage to the outer tubular body and/or to the inner metal core makes the roll difficult if not impossible to repair. It would be more economical if damaged portions of the roll could be replaced.
U.S. Pat. No. 3,006,625 teaches a conveyor roll having an outer high temperature shaft and an inner water cooled shaft connected at one end by a camming device so that thermal expansion of the outer shaft moves the outer shaft longitudinally of the inner shaft in a direction away from the inter-connected end. A limitation of the preceding type roll is the use of water circulating facilities. The water tight couplings and water circulating facilities add additional expense to the cost and maintenance of the rolls.
U.S. Pat. No. 3,608,876 teaches rollers including an outer tubular ceramic member packed with insulation. A driving and supporting shaft is connected to each end of the ceramic member. A limitation of this type of roller is that any damage to the ceramic member requires replacement of the member. Although the insulation and support shafts may be reused, the replacement of the outer tubular member makes the repair of this roller economically unacceptable.
U.S. Pat. No. 3,775,087 teaches tubular conveying rolls for use in the chilling section of a sheet glass tempering apparatus. The rolls included braided sleeve coverings and the hollow interior partially filled with lead shot to dampen unwanted vibrations. Although these rolls are suitable for reducing the frequent fracture of supported glass sheets during tempering, such rolls are not usually used in a glass annealing lehr. This is because roll vibration, if any, causes little, if any, problem.
U.S. Pat. Nos. 3,853,525; 3,877,919 and 4,216,005 each teach, in one form or another, a roll for supporting and conveying a glass substrate at elevated temperatures. In general, the roll includes a plurality of asbestos discs joined together and an outer cover, e.g., of boron nitride or polyamides or the discs impregnated with a solution of potassium sulfate to provide a lubricated roll surface and retard deterioration of the discs. Although these rolls are acceptable for their intended purposes, a limitation is that the asbestos discs are not generally acceptable for health considerations. Although discs made of pressed ceramic fibers can be used in place of the asbestos discs, they do not have the durability of the asbestos discs thereby decreasing the usable life of the roll.
As can now be appreciated, it would be advantageous to provide a roll for conveying and supporting a glass substrate, in particular, a continuous glass ribbon advancing through an annealing lehr that does not have the limitations of the presently available conveying rolls.